Band-filter device



July 8 1941. w, HAGEN 2,248,754

BAND-FILTER DEVICE Fil ed June 9, 1938 ill? W E a I hie/710w: 'l'i obga/ryflaym Patented Juiy 8, 1941 BAND FILTER DEVICE Wolfgang Hagen, Berlin, Germany, assignor to C. Lorenz Aktiengesellschaft, Berlin-Tempe] hof, Germany, a company Application June 9, 1938, Serial No. 212,753

7 In Germany June 11, 1937 :6 Claims.

The present invention relates to band-filter devices, and more particularly to adjustable band-filters adapted for wire-radio operation.

The heretofore known band-filters which have an adjustable width of pass band present the disadvantage that an adjustment of the bandfilter passing range requires the use of special aligning equipment and metering instruments. For example, band-filter equipped broadcasting receiving devices cannot be tuned in the simple manner which is employed in tuning broadcasting receiving devices which have resonance circuits, that is by tuning to the volume maximum. The reason why this simple manner of tuning is insufiicient for receivers employing band pass filters is that the carrier frequency must be located in the center of the passing range in order to enforce the band-filter eifect.

The present invention has for its object to provide a variable band-filter which is specifically well adapted for use in wire-radio system and which is adjustable in the most simple way. This novel band-filter comprises a plurality of tuned circuit, which are merely tuned as resonant circuits in accordance with any known method and which after the tuning has been accomplished are detuned with respect to one another by a simple switching operation so as to constitute a band-filter.

The arrangement according to the present invention involves the advantage that the adjustments may be made in a similar manner as normal resonance circuits, that is, by means of a simple amplitude indicator or by observing the loudness of the signals. The detuning of the resonance circuits, may, for instance, be accomplished in such manner that the circuits after having been tuned to the same frequency are detuned relative to each other by varying the capacities and/or the inductances forming these circuits.

The invention will be more readily understood from the following description taken in conjunction with the accompanying drawing, the single figure of which shows a wiring diagram according to one embodiment of the invention. The arrangement illustrated comprisesan amplifier arrangement in a. wire-radio system in which three difierent carrier waves are amplified in tuned amplifiers. These carrier frequencies are impressed upon the line a, b and applied to the amplifiers VI, V2 and V3 through the filtering devices I, II and III, and then conveyed to the outgoing line 0, d, common thereto through the output filters Fl, F2 and F3. Filter devices employed in such systems must be rendered adjustable for the purpose of permitting in a simple manner the filters of the appertaining amplifier to be matched to the frequency of its carrier wave in cases that this frequency should by any reasons be subjected to changes.

A band-filter according to the present invention is hereinafter more precisely explained in conjunction with the filter I of the figure. This filter consists of two resonance circuits KI and K2, each of which comprises inductances simultaneousl acting as transformer windings, and three fixed condensers which permit adjustment to three frequency ranges. The condensers of the resonance circuit Kl are designated Cl, C2 and C3, while those of the resonance circuit K2 are denoted Ci, C2 and C3. The frequency adjustment of these circuits Within each of the separate frequency ranges is accomplished by means of the variable condensers C and C, respectively. Additional balancing condensers ct, c2 and 03 are connected in shunt relation to said fixed condensers. Both resonance circuits KI and K2 are balanced to the maximum amplitude of the carrier wave in the state of parallel connection as illustrated in the drawing by way of an example, that is, with the condenser Clv shunted across the condenser cl.

After finished adjustment of the circuits to the carrier frequency the condenser cl is disconnected from the condenser Cl by interrupting the connection e and establishing the connection f. This operation which may be effected by means of a simple switch '9, places the balancing condenser cl parallel to the condenser CI of the resonance circuit K2 with the result that the two resonance circuits KI and K2 are detuned to one another, since the circuit Kl is tuned to a higher natural frequency, whereas the circuit K2 is tuned to a lower natural frequency whereby a band-filter is obtained. The additional condensers cl, c2 and 03 are so dimensioned with respect to the condensers CI to C3 that the width of the frequency band is constant in the three different ranges above referred to. Moreover, the condensers CI to C3 and CI to C3 are dimensioned in such manner that the frequencies of the circuits are shifted by the same amount in cases that the condenser C2 or C3 is connected instead of condenser CI. The width of the band may be adjusted at will by suitably dimensioning the various condensers.

The embodiment shown in the drawing discloses the inventive idea in connection with two resonance circuits, but the principle of the invention is applicable even if three or more resonance circuits are used.

In a filter arrangement having three resonance circuits, one of these circuits remains tuned to the carrier wave during the detuning operation, while the natural frequencies of the two other circuits are shifted with respect to the frequency of the first mentioned circuit. If four resonance circuits are provided, two circuits are shifted to a frequency higher than the carrier frequency and two of said circuits are shifted to a frequency below that of the carrier. The circuits of the band-filter may be arranged either in front of or behind its allotted amplifier.

According to a further feature of the invention, the reversibly switchable condenser may be coupled to one or more of the variable condensers so as to be rendered continually variable.

What is claimed is:

1. An adjustable band-filter device comprising inductances and variable capacities forming first and second resonance circuits tuned to the same frequency, additional fixed capacities allotted to each of said two resonance circuits, means for selectively interposing said additional capacities in their appertaining resonance circuits, further fixed capacities, means for selectively associating one of said further fixed capacities with said first a resonance circuit and means for transposing said one of said further fixed capacities from said first resonance circuit to said second resonance circuit so as to increase the natural frequency of said first circuit and to decrease the natural frequency of said second circuit.

2. An adjustable band-filter device as defined in claim 1, in which the further fixed capacities common to said resonance circuits are so dimensioned that the frequency of said circuits is shifted by the same amount.

3. An adjustable band-filter device as defined in claim 1, having means for mechanically coupling said one of said further fixed capacities with at least one of said variable capacities for rendering said operative condenser continually variable.

4. An adjustable band-filter device comprising inductances and variable capacities forming first and second resonance circuits tuned to the same frequency, further fixed reactances, at least one of said fixed reactances being connected in said first circuit and means for switching said one of said fixed reactance from said first circuit to said second circuit to operate therewith and increase the natural frequency of said first circuit and decrease the natural frequency of said second circuit.

5. An adjustable band-filter device comprising inductances and variable capacities forming first and second resonance circuits tuned to the same frequency, further fixed inductances, at least one of said fixed inductances being connected in said first circuit and means for switching said one of said fixed inductances from said first circuit to said second circuit to operate therewith and increase the natural frequency of said first circuit and decrease the natural frequency of said second circuit.

6. An adjustable band-filter device comprising inductances and variable capacities forming first and second resonance circuits tuned to the same frequency, further fixed capacities, at least one of said fixed capacities being connected to said first circuit and means for switching said one of said fixed capacities from said first circuit to said second circuit to operate therewith and increase the natural frequency of said first circuit and decrease the natural frequency of said second circuit.

WOLFGANG HAGEN. 

